This invention relates to the processing of foods and more particularly to improved methods of drying nuts.
Processed nuts are heated for a variety of reasons. Nuts are sometimes heated with boiling water (blanched) to promote easy removal of the shells. Heating of the nuts by blanching is usually performed at or above the boiling temperature of water for times approaching an hour. Nuts are sometimes dried to provide increased shelf life, to produce a readily edible food product, or to prepare the nuts for further cooking steps. Methods of drying include roasting, such as where the nut is heated in oil to temperatures from about 250 to 375 F.
While heating has many beneficial uses, it may also produce undesirable side effects including: discoloration; unacceptable changes in texture or consistency; rancidity or other reactions that shorten shelf life; and driving tannins or other acids from the shell into the nutmeat during blanching. Of particular concern here are heat induced rancidity and shortened shelf life that often occur in acid-containing nuts.
Specifically, the drying of some types of nuts, such as walnuts that contain high levels of tannins or other acids, is problematic (L. Jurd, Journal of the American Chemical Society, volume 78, page 3445, 1956) due to enzymatic activity and reactions between acids and oils within the nut. For example, roasting walnuts produces a nut that either quickly becomes rancid or that has an unacceptable shelf life. As a result roasted walnuts are not widely available.
Roasting is one well-known method of drying foods. For example, peanuts and nuts such as almonds, cashews, pecans and macadamias are cooked in oil at temperatures above the boiling point of water, sometimes in the presence of seasonings such as salt. Unfortunately temperatures significantly above the boiling point of water can induce reactions between nut oils and acids, tannin in particular, resulting in a rancid nut. Nuts with high fatty acid content include: walnuts, cashews, pecans and macadamias. Even in nuts without high acid content, roasting can introduce surface blemishes. This problem has been addressed, for example, by Renner et al. (U.S. Pat. No. 3,457,087) by quenching the nuts to a lower temperature of about 130 F. While the method of Renner et al. addresses the appearance of the nuts, the problems associated with heating tannin-containing nuts remain.
Blanching has been used as a method of shelling nuts; see for example U.S. Pat. No. 2,558,899 to Green. Nuts are exposed to water at or above its boiling point to soften the shells prior to removal. Green noted that during blanching tannins are removed from the shells, and recommended limiting the blanching time to prevent tannins from migrating from the blanching water into the nutmeat. If further processing of the nut includes roasting, migration of tanning from the shell to the nuts may result in the previously noted rancidity problems.
The problems with heating acid-containing nuts may be reduced by removing the tannins from the nut. In a patent related to the removal of tannins from nutmeats, Invernizzi et al. (U.S. Pat. No. 4,160,044) disclose repeated exposure of nuts to demineralized water, followed by drying the nuts. Specifically, Invernizzi et al. disclose removing tannins that might produce discoloration of other food products, such as processed cheeses, that are in contact with the nuts. The process includes removing tannins by three separate, low temperature, demineralized immersion baths of nutmeats over a period of 22 to 24 hours. While this process apparently removes the tannins, and thus could be used prior to roasting, it is a complicated and time-consuming process.
While these methods address some of the issues resulting from heating nuts, none of these methods addresses all of the problems encountered in the commercial-scale drying of nuts having high concentrations of tannic acid and high concentrations of lipid or fatty acids. The application of the previously described methods to walnuts, for example, results in walnuts that are rancid, have unacceptably short shelf-life (days or months), must be refrigerated or otherwise exposed to other hard to control environments, or must be subjected to a long and complicated process.
Walnut growers, in particular, find that the difficulties involved in commercially roasting walnuts is a hindrance to their sale as a prepared food product or as a snack food. Thus, for example, while roasted walnuts can be eaten soon after roasting or can be refrigerated for later use, they are not found in large quantity, commercially available snack foods, such as in roasted nut mixtures. In view of the above-mentioned limitations in the food preparation arts, there is a need for a method of processing high fatty acid containing and tannic acid containing nuts, such as walnuts in particular, which results in a dry nut that can be stored or packaged for later use or for snack food consumption.
It is one aspect of the present invention to provide a method of processing nuts to drive off a substantial fraction of high fatty acids from the nuts, followed by drying. The reduction of the acid concentration in the nut prior to drying allows for a greater range of drying conditions. The process of the present invention is particularly useful, though not limited to, nuts having high fatty acid content and tannic acid. In addition, the process of the present invention is less time consuming, than other processes that remove tannins from food products, is compatible with commercial nut operations, and removes tannins that may cause a bitter taste. One embodiment of the process includes blanching the nuts to remove acids therein and drying the nuts to a partially dehydrated state.
It is another aspect of the invention to provide a method whereby shelled nuts are heated to stop enzymatic activity and removed acids from nuts without causing the nut oils to react and to reduce the nuts to a partially dehydrate state. In one embodiment, nuts are heated less than 5 minutes in water at a temperature of less than 280 F. to stop enzymatic activity and remove acids, and are then dried at a temperature of less than 280 F. until the water content becomes 5% or less, preferably 2% or less.
It is another aspect of the present process to protect the dehydrated nuts from further reactions by coating the nuts. In one embodiment, the dehydrated nuts are coated with a glaze to inhibit reactions of the nut with the atmosphere. The glazed nut is then stored in a container that is substantially free of oxygen and light.
It is yet another aspect of the present invention to produce dried nuts having reduced quantities of tannic acid a process that is rapid and is compatible with current commercial nut processes.
All publications and patents cited herein are hereby incorporated by reference in their entirety for all purposes. Additional objects, advantages, aspects and features of the present invention will become apparent from the description of the invention, set forth below, which should be taken in conjunction with the accompanying drawings, a brief description of which follows.